Pin 'mpmath<1.4' in CI (#8291)

Author: NicolasHug

.github/scripts/setup-env.sh

@@ -87,7 +87,8 @@ case $GPU_ARCH_TYPE in
     ;;
 esac
 PYTORCH_WHEEL_INDEX="https://download.pytorch.org/whl/${CHANNEL}/${GPU_ARCH_ID}"
-pip install --progress-bar=off --pre torch --index-url="${PYTORCH_WHEEL_INDEX}"
+# TODO: remove pinning of mpmath when https://github.com/pytorch/vision/issues/8292 is properly fixed.
+pip install --progress-bar=off "mpmath<1.4" --pre torch --index-url="${PYTORCH_WHEEL_INDEX}"
 
 if [[ $GPU_ARCH_TYPE == 'cuda' ]]; then
   python -c "import torch; exit(not torch.cuda.is_available())"